我在编写并行MPI I/O程序时遇到了问题,该程序将以特定的模式写入。我能够让进程0写入整数0-9,进程1写入整数10-19,进程2写入整数20-29,等等。
proc 0: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
proc 1: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
proc 2: [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]
proc 3: [30, 31, 32, 33, 34, 35, 36, 37, 38, 39]
result: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
下面是实现这一点的代码:
int main(int argc, char *argv[]) {
// MPI_Finalize();
int i, rank, size, offset;
MPI_File fhw;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
int N = size * 10;
int buf[N];
for ( i = 0; i < N; ++i ) {
buf[i] = rank * 10 + i;
}
offset = rank * (N/size) * sizeof(int);
MPI_File_open(MPI_COMM_WORLD, "datafile", MPI_MODE_CREATE|MPI_MODE_WRONLY,
MPI_INFO_NULL, &fhw);
printf("(%d) Writing to file...\n", rank);
printf("\nRank: (%d), Offset: %d\n", rank, offset);
MPI_File_write_at(fhw, offset, buf, (N/size), MPI_INT, &status);
MPI_File_close(&fhw);
MPI_Finalize();
return 0;
}
但是,我对如何产生以下结果感到困惑:
// starting out:
proc 0: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
proc 1: [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
proc 2: [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]
proc 3: [30, 31, 32, 33, 34, 35, 36, 37, 38, 39]
// proc 0 writes first 2 slots, then proc 1 writes next 2, etc.
result: [0, 1, 10, 11, 20, 21, 30, 31, 2, 3, 12, 13, 22, 23, ..., 8, 9, 18, 19, 28, 29, 38, 29]
在过去的几个小时里,我在网上查找示例和文档时尝试使用MPI_File_set_view
,但无法正常工作。有人能给我指引正确的方向吗?
发布于 2019-03-20 08:12:55
正如您所了解的那样,您需要设置一个视图...
然后是代码中的一些小错误: 1)每个进程真的需要大于10的buf吗? 2) MPI_File_wite_at中的偏移量是以字节为单位的,但以元素的数量为单位(就视图的元素大小而言)。
因此,要设置视图,只需要一行代码:
#include "mpi.h"
#include <cstdio>
int main(int argc, char *argv[]) {
// MPI_Finalize();
int i, rank, size, offset;
MPI_File fhw;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
int N = 10;
int buf[N];
for ( i = 0; i < N; ++i ) {
buf[i] = rank * 10 + i;
}
offset = 10*rank;
MPI_File_open(MPI_COMM_WORLD,"datafile",MPI_MODE_CREATE|MPI_MODE_WRONLY,
MPI_INFO_NULL, &fhw);
printf("(%d) Writing to file...\n", rank);
printf("\nRank: (%d), Offset: %d\n", rank, offset);
MPI_File_set_view( fhw,0,MPI_INT, MPI_INT, "native", MPI_INFO_NULL ) ;
MPI_File_write_at(fhw, offset, buf, N, MPI_INT, &status);
MPI_File_close(&fhw);
MPI_Finalize();
return 0;
}
然后,您可以使用MPI_File_write :-)执行完全相同的操作,并为每个进程设置不同的视图,只需替换视图并编写:
MPI_File_set_view(fhw,offset*sizeof(int),MPI_INT,MPI_INT,
"native",MPI_INFO_NULL ) ;
MPI_File_write_at(fhw, 0, buf, N, MPI_INT, &status);
或者简单地说:
MPI_File_set_view(fhw,offset*sizeof(int),MPI_INT,MPI_INT,
"native",MPI_INFO_NULL ) ;
MPI_File_write(fhw, buf, N, MPI_INT, &status);
注意:在视图中,偏移量是以字节为单位的,而在写入中,它是以视图元素的大小为单位的……可能有点困惑:-)
然后是魔术:
你需要写2个整数大小为2*的块,你有N/2个这样的块,所以你创建一个类型:
MPI_Type_vector(N/2, 2 , size*2, MPI_INT, &ftype);
MPI_Type_commit(&ftype);
并设置视图:
MPI_File_set_view( fhw, rank*2*sizeof(int), MPI_INT, ftype, "native", MPI_INFO_NULL ) ;
然后你必须认为在内存中你有一个连续的数据存储,为了适合你的视图,它必须是N/2个块的东西,所以你创建了一个数据类型:
MPI_Type_contiguous(2, MPI_INT, &mtype);
MPI_Type_commit(&mtype);
然后你就可以开始写了:
MPI_File_write(fhw, buf, N/2, mtype, &status);
MPI_File_close(&fhw);
因此,整个代码将变成:
#include "mpi.h"
#include <cstdio>
int main(int argc, char *argv[]) {
int i, rank, size, offset;
MPI_File fhw;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
int N = 10; //need to be even!!!
int buf[N];
for ( i = 0; i < N; ++i ) {
buf[i] = rank * N + i;
}
offset = 10*rank;
MPI_File_open(MPI_COMM_WORLD, "datafile", MPI_MODE_CREATE|MPI_MODE_WRONLY,
MPI_INFO_NULL, &fhw);
printf("(%d) Writing to file...\n", rank);
printf("\nRank: (%d), Offset: %d\n", rank, offset);
MPI_Datatype ftype,mtype;
MPI_Type_vector(N/2, 2 , size*2, MPI_INT, &ftype);
MPI_Type_commit(&ftype);
MPI_File_set_view( fhw, rank*2*sizeof(int), MPI_INT, ftype,
"native",MPI_INFO_NULL ) ;
MPI_Type_contiguous(2, MPI_INT, &mtype);
MPI_Type_commit(&mtype);
MPI_File_write(fhw, buf, N/2, mtype, &status);
MPI_File_close(&fhw);
MPI_Finalize();
return 0;
}
https://stackoverflow.com/questions/55235929
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